1. Filed of the Invention
The present invention relates to zirconium and hafnium metal precursors useful for chemical vapor deposition (CVD) of Zr/Hf doped gate dielectric, high dielectric constant (k) and/or ferroelectric metal oxide thin films.
2. Description of the Related Art
Zirconium and hafnium-containing silicates possess dielectric constant (k) values in the range of from about 10 to 15, and therefore are highly useful as gate dielectric materials in various microelectronic structures and devices. Zirconium- and hafnium-doped ferroelectric or high dielectric constant complex metal oxides, such as Pb(Zr,Ti)O3, are also being considered for the manufacturing of microelectronic devices.
In such applications, the choice of zirconium or hafnium source reagents is of critical importance for the successful chemical vapor deposition of high quality Zr/Hf-doped gate dielectric or high dielectric constant metal oxide thin films.
Fabrication of high quality Zr/Hf doped gate dielectric, high dielectric constant and/or ferroelectric metal oxide thin films requires that the zirconium or hafnium CVD source reagents so employed produce a clean interface between the substrate surface and the Zr/Hf thin films deposited thereon. Deleterious occurrence of side reactions, e.g., when the substrate is silicon, produce predominantly silicon dioxide (SiO2), locally doped SiO2, and/or other surface impurities, are desirably minimized, because formation of such surface impurities reduces the capacitance and therefore compromises performance of the deposited gate dielectric, high dielectric constant and/or ferroelectric metal oxide thin films.
Further, the Zr/Hf source reagents must be thermally stable to avoid premature decomposition of such source reagents before they reach the CVD reaction chamber during the CVD process. Premature decomposition of source reagents not only results in undesirable accumulation of side products that will clog fluid flow conduits of the CVD apparatus, but also causes undesirable variations in composition of the deposited gate dielectric, high dielectric constant and/or ferroelectric metal oxide thin film.
Moreover, the Zr/Hf source reagents have to be chemically compatible with other source reagents used in the CVD process. xe2x80x9cChemically compatiblexe2x80x9d means that the Zr/Hf source reagents will not undergo undesirable side reactions with other source reagents, e.g., reagents containing silicon or other metals, such as Pb and/or Ti.
Finally, the Zr/Hf source reagents must be able to maintain their chemical identity over time when dissolved or suspended in organic solvents. Any change in chemical identity of source reagents in the solvent medium is deleterious since it impairs the ability of the CVD process to achieve repeatable delivery and film growth.
There is a continuing need in the art to provide improved Zr/Hf source reagents suitable for high efficiency CVD processes, for fabricating corresponding high quality Zr/Hf-doped gate dielectric, high dielectric constant and/or ferroelectric metal oxide thin films.
The present invention broadly relates to a Zr/Hf source reagent composition having utility for forming dielectric thin films such as doped gate dielectrics, high dielectric constant metal oxides and/or ferroelectric metal oxides, and to a chemical vapor deposition (CVD) method for deposition of Zr or Hf utilizing such composition.
The invention in one aspect relates to a Zr/Hf source reagent composition of the formula: 
In such formula, M denotes zirconium or hafnium. Each of R1, R2, R3, and R4 is independently selected (i.e., it can either be the same as or different from other(s) of the R1, R2, R3, and R4 substituents) from the group consisting of H, aryl, perfluoroaryl, C1-C8 alkyl, and C1-C8 perfluoroalkyl. R5 and R6 are both tert-butyl (tBu).
As used herein, the term xe2x80x9cthin filmxe2x80x9d refers to a material layer having a thickness of less than about 1000 microns.
In a specific aspect of the present invention, the Zr/Hf metal precursor comprises at least one xcex2-diketonate moiety. Illustrative xcex2-diketonate moieties include the following:
One particularly preferred Zr/Hf metal precursor species of the present invention has the formula M(thd)2(O-tBu)2 wherein M is Zr or Hf. In such precursor, the bulky t-butyl groups function to minimize deleterious isomerization reactions and enhance thermal stability of the precursor. The preferred M(thd)2(O-tBu)2 precursor can be synthesized by reacting M(O-tBu)4 with two equivalents of Hthd in a dry hydrocarbon or aryl solvent according to the following equation:
M(O-tBu)4+2Hthd M(thd)2(O-tBu)2+2HO-tBu 
Another aspect of the present invention relates to a CVD source reagent composition comprising a Zr/Hf metal precursor as described hereinabove, and a solvent medium in which the Zr/Hf metal precursor is soluble or suspendable. Providing a source reagent composition in liquid (e.g., solution or suspension) form facilitates rapid volatilization (e.g., flash vaporization) of the source reagent composition and transport of the resultant precursor vapor to a deposition locus such as a CVD reaction chamber. Further, when used in solution the precursor stability is greatly improved over other prior art alcoxide analogs.
The solvent medium utilized in the CVD source reagent composition may comprise any suitable solvent species, or combination of solvent species, with which the metal precursor(s) are compatible. Such solvent medium may for example comprise ethers, glymes, tetraglymes, amines, polyamines, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, cyclic ethers, or compatible combinations of two or more of the foregoing solvents.
A particularly preferred solvent species useful in the practice of the present invention is octane.
In yet another aspect, the invention relates to a method of forming a Zr/Hf dielectric thin film on a substrate, wherein the dielectric thin film is selected from the group consisting of doped gate dielectric, high dielectric constant metal oxide and ferroelectric metal oxide, comprising the following steps:
vaporizing a source reagent composition comprising a Zr or Hf metal precursor to form a source reagent precursor vapor;
transporting such source reagent precursor vapor into a chemical vapor deposition zone, optionally using a carrier gas;
contacting the substrate with the source reagent vapor in the chemical vapor deposition zone in the presence of an oxidizer and at elevated temperature, to deposit a corresponding Zr- or Hf-containing thin film on the substrate, e.g., a doped gate dielectric thin film, a high dielectric constant metal oxide thin film and/or a ferroelectric metal oxide thin film;
wherein the Zr or Hf metal precursor has the following formula: 
wherein:
M is Zr or Hf;
each of R1, R2, R3, and R4 is independently selected from the group consisting of H, aryl, perfluoroaryl, C1-C8 alkyl, and C1-C8 perfluoroalkyl; and
R5 and R6 are both t-butyl groups.
The step of vaporizing the source reagent composition comprising the Zr/Hf metal precursor is preferably carried out at a vaporization temperature in the range of from about 100xc2x0 C. to about 300xc2x0 C. Within this narrow range of vaporization temperature, the Zr/Hf metal precursor is effectively vaporized with a minimum extent of premature decomposition.
In the optional use of a carrier gas in the practice of the present invention, for transporting the vaporized source reagent composition into the chemical vapor deposition zone, suitable carrier gas species include gases that do not adversely affect the metal-containing film being formed on the substrate. Preferred gases include argon, helium, krypton or other inert gas, with argon gas generally being most preferred. In one illustrative embodiment, argon gas may be introduced for mixing with the vaporized source reagent composition at a flow rate of about 100 standard cubic centimeters per minute (sccm).
Oxidizers useful for the broad practice of the present invention include, but are not limited to, O2, N2O, and O3. More preferably, the oxidizer used comprises oxygen, and in one illustrative embodiment corresponding to the argon flow rate illustratively described above, oxygen is introduced into the chemical vapor deposition zone at a flow rate of about 700 sccm.
The deposition of the Zr/Hf-containing dielectric thin film is preferably carried out under an elevated deposition temperature in a range of from about 300xc2x0 C. to about 750xc2x0 C.
Other aspects, features, and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.